Pete Edwards took a punt on his grand-son when he was only 18 months old, betting 50 pounds that he would play for Wales at odds of 2,500-1.
Wilson came on for his first appearance in the 87th minute of Wales's 1-1 draw with Belgium in a World Cup qualifier on Tuesday.
He was 16 years and 207 days, breaking the record of Gareth Bale, the world's most expensive footballer, as the country's youngest player by 108 days.
"Mr Edwards has been able to quit his job as a result of his amazing ability to spot fledgling talent earlier than almost anyone else we've ever taken a bet from," Graham Sharpe, a spokesman for bookmaker William Hill, said in a statement.
"Apparently, England have also been interested in Harry, who has a grandmother born in Chester. If (England manager) Roy Hodgson had snapped him up this bet would have been a loser!"